Method of bonding pencil leads to pencil sheaths



March 30, 1965 METHOD OF BONDING PENCIL LEADS TO PENCIL SHEATHS E. GOSSEL Filed July 25. 1961 O OAIIING THE BAKED UNTREATED LEAD WITH ADHESIVE COMPRISING AN.. EVAPORABLE DILUTANT.

D RYING THE" COATING TO REMOVE THE DILUTANT AND RENDER THE COATING MICRQBDBQLLS A.

CAUSING PENETRATION OF AFATTY vAGENT THROUGH THE PORES OF THE ADHESIVE COATING INTO THE LEAD REM VING ANY EXCESS FA TY AGENT FROM THE SURFACE OF THE LEADI INVENTOR.

EDGAR GOSSEL ATTORNEY United States Patent 31,808 9 Claims. (Cl. 12083) The present invention relates to the manufacture of pencils and more particularly to a method of intimately bonding a pencil lead, and especially a baked lead which after baking is impregnated with a fat solution, to the pencil sheath by means of an adhesive.

Pencil leads of the prior art treated with fat solutions can not be intimately bonded to their wooden sheaths because of lack of afiinity between glue and fat. As a result thereof when such a pencil is used the lead slides relative to and into the sheath under the writing pressure. Such insufficient bonding has the further disadvantage that the connection between the lead point and the wooden tip of the sheath of a sharpened pencil is often so insecure that it does not sufficiently support the lead at this point. Thus, if a stronger writing pressure is applied, the lead breaks olf easily within the sharpened wooden tip and the latter often also breaks off.

In order to overcome these disadvantages it has been proposed to provide the lead with grooves or recesses filled with adhesive to attain a better bond. Another method to overcome the mentioned disadvantages employs sand-blasting the leads. These known methods are expensive and do not accomplish satisfactorily the desired result. This is especially due to the fact that the greasy surfaces of the lead, including those of the grooved portions thereof, do not permit a secure connection with the adhesive. Attempts have therefore been made to develop an improved method of bonding the lead and Wooden pencil sheath to each other by first applying a coating of adhesive only upon a part of the surface of the lead before the same is impregnated. This coating preferably has a honeycomb or gridlike shape and is applied by printing it upon the lead. During the impregnation, the fat can then penetrate through the unprinted surface areas only of the lead, which are free of adhesive, while in the subsequent cementing process a secure connection may be attained between the gridlike coating of adhesive and the wooden sheath. This method is very expensive since the printing of the individual leads has to be carried out in special apparatus or machines. It has the further disadvantage that a complete impregnation is attainable only, if the total surface area of the lead left uncoated by the adhesive pattern, is sufficiently large and absolutely free of adhesive. When this precaution is observed the connection of the adhesive on the lead to the wooden sheath is restricted to relatively small surfaces, the bond between the lead and the wooden sheath is insufficient, the method must be applied very carefully to prevent the lead from shifting within the sheath and the bonding connection still will not become uniform along the entire surface of the lead but exists only at certain points. This becomes detrimental at the point of connection between the rim of the wooden sheath surrounding the tip of the lead. The sheath there is very liable to breaking when a stronger writing pressure is applied to the pencil.

It is an object of the present invention to overcome the above-mentioned disadvantages of the prior art by intimately connecting the lead pencil with the pencil sheath into an integral body.

This is accomplished by providing the entire surface of the lead first with a microporous coating of adhesive,

3,175,538 Patented Mar. 30, 1965 while impregnating the lead through the microscopic pores of the adhesive coating only subsequently thereto in the usual manner.

The invention is illustrated in the accompanying drawing, the only figure of which is a diagrammatic showing of the basic steps involved.

The microporous adhesive is applied to the untreated lead surface by coating it. A suitably diluted solution of a synthetic-resin adhesive may be selected from those used conventionally in the pencil manufacture for cementing together the wooden strips of the pencil sheath; subsequently this coating on the lead 'is dried at an increased room temperature. By applying the adhesive upon the lead in a highly diluted condition and by thereafter drying it thereon so that the diluting water will evaporate, a microporous coating willbe formed on the pencil lead firmly anchored in the lead surface. After the lead is then impregnated in the conventional manner, the excess fatty impregnating substance is removed and the lead is thereupon cemented into the wooden sheath in the usual manner. By this cementing process the porous adhesive coating is slightly softened so that a homogeneous coating of adhesive is formed which covers the entire surface of the lead and firmly secures the lead and the wooden sheath to each other.

The effect of the fat penetrating through the layer of dried adhesive into the lead can be explained only by the fact that during the drying process fine pores are formed through which the impregnating fat penetrates, thus getting into direct contact with the pencil lead.

The method according to the invention may be carried out, for example, in the following manner:

The baked but otherwise untreated pencil leads are first immersed in a disperse emulsion of a synthetic resin adhesive which is highly diluted with water, for example, in a conventional polyvinyl acetate adhesive which is diluted at a ratio of l to 10, and the leads are left in this solution for a few minutes. The excess of the adhesive solution is then allowed to drip off or it is removed from the leads by centrifugal action so that only a thin coating remains thereon. The leads are then dried either in the conventional manner at an increased room temperature or by infrared radiation. Thereafter, the leads are impregnated in the usual manner with a fatty solution which penetrates through the microscopic pores of the adhesive coating. Any fat remaining on the surfaces of the leads after this treatment is then removed therefrom by means of a centrifuge and the action of steam. The leads are then ready to be cemented in the usual manner into the wooden sheaths.

The pencil leads which are treated in the aforementioned manner are securely bonded to the wooden sheaths at all points thereof and they are thus not only absolutely prevented from shifting within the wooden sheaths when a strong writing pressure is applied, but they are protected to a considerable extent fom breaking within the sheaths when the pencil is dropped, hit, or bent.

Micro-porous adhesive coatings, and the theory of their behaviors, as well as the selection of an appropriate adhesive compatible with an evaporable diluent, are within the knowledge of those skilled in the art of adhesives. This art including polyvinyl and other resins and glues, and also specifically polyvinyl acetate, discussed above, is dealt with for instance in the following publications: U.S. Patents Numbers 2,825,282 and 2,806,256, and books by John Delmonte Technology of Adhesives by Reinhold Publishing Corporation, New York City, 1948 edition, and by De Bruyne and Houvink, Adhesion and Adhesives, by Elsevier Publishing Co., 1951 edition.

Although my invention has been illustrated and de scribed with reference to a preferred embodiment thereof I wish to have it understood that it is in no way limited hesive and a Wood sheath-bonded'to the coating by an polyvinyl acetate adhesive.

3. A method of joining securely and intimately a .pencil lead and a pencil sheath into an integrally fused unit comprising the steps of:

(1) coating the baked lead along its surface with an adhesive highly diluted with Water the said adhesive being of the group of the Water-soluble synthetic resins;

(2) drying said adhesive coating on said lead to form an all over, uniform microporous coating;

(3') coating the said dried microporous adhesive on the lead with a fatty agent for impregnating the lead by the fatty agent and removing any fatty agent not adsorbed by the lead from its surface and (4) cementing the leadwithinthe sheath into an integrally fused unit by employing an adhesive of the type compatible with' the adhesive selected for coating said lead.

4. A method according to claim 3, the said adhesive being of the group of waterasoluble'polyvinyl adhesives.

5. A method according to claim 4, the adhesive being a polyvinyl-acetate adhesive.

6. A method as claimed in claim 3, wherein the ratio of dilution of the adhesive with Water is 1:10.

7. A method as claimed in claim 3, said step of coating the lead with adhesive including the step ofleaving the lead immersed in said adhesive for several minutes.

8. A method as claimed in-claim 3, in which the adhesive coating is dried on the lead under an increased room temperature.

9. A method as claimed in claim 3, the third step further comprising removing by centrifugal action and steam any fatty agent still adhering to the lead surface after the lead has been treated with the fatty solution.

. References Cited by the Examiner I UNITED STATES PATENTS 7/50 Grieco -83 3,086,903 4/63 Grossman l20.-273

EARL M. BERGERT, Primary Examiner. JOSEPH REBOLD, Examiner. 

1. A LEAD PENCIL COMPRISING A PENCIL LEAD COATED ALL OVER, UNIFORMLY WITH A GREASE PERVIOUS MICROPOROUS ADHESIVE AND A WOOD SHEATH BONDED TO THE COATING BY AN ADHESIVE COMPATIBLE THEREWITH. 